<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        // let age = 18 
        // age = age + 1
        //  age++

        // 1. 用户输入 
        let num = prompt('请您输入一个数字:')
        // 2. 判断输出- 小于10才补0
        // num = num < 10 ? 0 + num : num
        num = num >= 10 ? num : 0 + num
        alert(num)

//         let num = prompt('请您输入一个数字:')
//             num < 10 ? alert(0 + num) : alert(num)
    </script>
</body>

</html>